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title: Date.prototype.toJSON()
short-title: toJSON()
slug: Web/JavaScript/Reference/Global_Objects/Date/toJSON
page-type: javascript-instance-method
browser-compat: javascript.builtins.Date.toJSON
sidebar: jsref

The toJSON() method of {{jsxref("Date")}} instances returns a string representing this date in the same ISO format as {{jsxref("Date/toISOString", "toISOString()")}}.

{{InteractiveExample("JavaScript Demo: Date.prototype.toJSON()")}}

const event = new Date("August 19, 1975 23:15:30 UTC");

const jsonDate = event.toJSON();

console.log(jsonDate);
// Expected output: "1975-08-19T23:15:30.000Z"

console.log(new Date(jsonDate).toUTCString());
// Expected output: "Tue, 19 Aug 1975 23:15:30 GMT"

Syntax

toJSON()

Parameters

None.

Return value

A string representing the given date in the date time string format according to universal time, or null when the date is invalid. For valid dates, the return value is the same as that of {{jsxref("Date/toISOString", "toISOString()")}}.

Description

The toJSON() method is automatically called by {{jsxref("JSON.stringify()")}} when a Date object is stringified. This method is generally intended to, by default, usefully serialize {{jsxref("Date")}} objects during JSON serialization, which can then be deserialized using the {{jsxref("Date/Date", "Date()")}} constructor as the reviver of {{jsxref("JSON.parse()")}}.

The method first attempts to convert its this value to a primitive by calling its [Symbol.toPrimitive]() (with "number" as hint), {{jsxref("Object/valueOf", "valueOf()")}}, and {{jsxref("Object/toString", "toString()")}} methods, in that order. If the result is a non-finite number, null is returned. (This generally corresponds to an invalid date, whose {{jsxref("Date/valueOf", "valueOf()")}} returns {{jsxref("NaN")}}.) Otherwise, if the converted primitive is not a number or is a finite number, the return value of {{jsxref("Date/toISOString", "this.toISOString()")}} is returned.

Note that the method does not check whether the this value is a valid {{jsxref("Date")}} object. However, calling Date.prototype.toJSON() on non-Date objects fails unless the object's number primitive representation is NaN, or the object also has a toISOString() method.

Examples

Using toJSON()

const jsonDate = new Date(0).toJSON(); // '1970-01-01T00:00:00.000Z'
const backToDate = new Date(jsonDate);

console.log(jsonDate); // 1970-01-01T00:00:00.000Z

Serialization round-tripping

When parsing JSON containing date strings, you can use the {{jsxref("Date/Date", "Date()")}} constructor to revive them into the original date objects.

const fileData = {
  author: "Maria",
  title: "Date.prototype.toJSON()",
  createdAt: new Date(2019, 3, 15),
  updatedAt: new Date(2020, 6, 26),
};
const response = JSON.stringify(fileData);

// Imagine transmission through network

const data = JSON.parse(response, (key, value) => {
  if (key === "createdAt" || key === "updatedAt") {
    return new Date(value);
  }
  return value;
});

console.log(data);

The reviver of JSON.parse() must be specific to the payload shape you expect, because the serialization is irreversible: it's not possible to distinguish between a string that represents a Date and a normal string.

AbdulElahGwaith
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